By Jessica Firger
October 2, 2015
|Another study shows that vaccines don't cause autism.|
Most experts today agree that the belief that childhood vaccines cause autism is based on bunk science. Even still, some advocacy groups claim immunizations are responsible for raising the risk for this neurodevelopmental condition, despite a growing body of research that shows there isn’t a link.
(The study that most anti-vaccination groups point to was retracted after it was found to be based on falsified data.)
Despite the science, organizations involved in the anti-vaccine movement still hope to find some evidence that vaccines threaten children’s health. For example, the autism advocacy organization SafeMinds recently funded research it hoped would prove vaccines cause autism in children. But this effort appears to have backfired for the organization—whose mission is to raise awareness about how certain environmental exposures may be linked to autism—since the study SafeMinds supported showed a link between autism and vaccines does not exist.
Between 2003 and 2013, SafeMinds provided scientists from the University of Texas Southwestern School of Medicine, the University of Washington, the Johnson Center for Child Health & Development and other research institutions with approximately $250,000 to conduct a long-term investigation evaluating behavioral and brain changes of baby rhesus macaques that were administered a standard course of childhood vaccines. (The National Autism Association, another organization that has questioned vaccine safety, also provided financial support for this research.)
The latest paper in the multiyear project was published Monday in the Proceedings of the National Academy of Sciences (PNAS). In it, the researchers concluded that vaccines did not cause any brain or behavioral changes in the primates.
The PNAS paper reports findings of the full-size study, conducted between 2008 and 2014 at the Washington National Primate Research Center, that occurred after the completion of an initial pilot program on 17 infant macaques. The full study involved 79 infant male macaques, aged 12 to 18 months, broken into six groups. Two groups received thimerosal-containing vaccines for a child’s complete vaccine schedule; two were given the measles, mumps and rubella (MMR) vaccine without TCVs; and two received saline injections as a control group.
In each case, the monkeys were further split into subgroups: half were on an accelerated vaccination schedule recommended by the U.S. Centers for Disease Control and Prevention in the 1990s, and half were on the recommended schedule from 2008.
Anti-vaccine activists have claimed that both the vaccines with thimerosal—a mercury-based antifungal and antiseptic preservative—and the MMR vaccines are linked to autism. Thimerosal was removed from most vaccines in the late 1990s. But the researchers wanted to study its potential health effects anyway.
The researchers then put the monkeys together in cages to see if they exhibited any new autistic-like social behaviors, such as fear, withdrawal, rocking, self-clasping and stereotypy (repetitive behavior). They reported that the monkeys’ behaviors remained unchanged.
(Another paper by some of the same researchers, published in February in Environmental Health Perspectives, assessed the learning and social behaviors of the same group of monkeys and found the vaccines did not affect their development.)
For the PNAS paper, the researchers also conducted postmortem analyses of the primates’ brains after they had been euthanized. The team looked for brain abnormalities, including those in the volume and density of the cerebellum, amygdala and hippocampus regions, all of which have been shown to have some variations in children with autism. They also looked at the numbers and size of certain types of brain cells, known as Purkinje cells; some studies have shown there are fewer Purkinje cells in the brains of children with autism.
The researchers say they didn’t find any marked differences in the brains of monkeys in the vaccine groups compared with those in the control group.
SafeMinds, the nonprofit that funded the research, is not happy with the results. Representatives from the group say the findings contradict both an earlier pilot study and interim progress reports the organization received from the researchers.
The pilot study, undertaken at the University of Pittsburgh, led to two papers, both published in 2010, showing that the vaccines did in fact affect brain development in infant macaques. One paper, published in Acta Neurobiologiae Experimentalis, looked at the development of the amygdala region of the brains of monkeys that received the complete U.S. childhood vaccine schedule from the 1990s and then underwent MRI and PET scans at 4 and 6 months of age.
The researchers reported that amygdala volume was different in monkeys that received the vaccines versus those that did not. They also reported differences in certain opioid receptors in the brains of monkeys in the vaccine group. The other paper, from the Journal of Toxicology and Environmental Health, looked at differences in the reflexes of baby monkeys that received a single dose of thimerosal-containing hepatitis B vaccine versus those in a control group.
In that paper, the researchers reported that “in exposed animals there was a significant delay in the acquisition of root, snout, and suck reflexes, compared with unexposed animals.”
SafeMinds argues that these changes all suggest a correlation between vaccination and autism. But as Alycia Halladay, chief science officer at the Autism Science Foundation, points out, these findings do not necessarily indicate anything about autism. “There are likely many biological effects that occur in an organism after a vaccine administration, but that doesn’t always mean it will cause autism,” she says.
SafeMinds also believes that the research team behind the new PNAS study may have cherry-picked their data. SafeMinds Director Lyn Redwood, a registered nurse, says she received an email in 2013 from the researchers reporting a “statistically significant” 11 percent reduction in certain types of hippocampal cells in the vaccine groups. But she says the authors did not include these findings in the new paper.
Dr. Laura Hewitson, director of research for the Johnson Center for Child Health & Development, an adjunct associate professor in the Department of Psychiatry at the University of Texas Southwestern Medical Center, a lead researcher on project and co-author on all four papers, says that at the time that email was sent, it was also made clear to SafeMinds “that the data should be treated as preliminary until all of the animals had completed the study.” She added that none of the study’s procedures changed once her team moved from the pilot program to a larger sample.
“The same assessments were performed on a much larger number of primates by a team of behaviorists with decades of experience working with nonhuman primate infants,” Hewitson tells Newsweek. “For example, in the pilot study we examined 13 different neonatal reflexes from birth to 14 days of age in just two groups of animals. In the current study, we examined those same 13 reflexes, plus six others from birth to 21 days of age, in six groups of animals—a much more comprehensive experimental design.”
She added that all of the researchers, technicians and behaviorists involved in collection and analysis of data did not know which of the monkeys were in the vaccine groups or the control group. The researchers also implemented a “chain of custody” protocol once the data were collected, in which they reviewed chronological documentation that shows the control, transfer and analysis of all data sets. Hewitson says that her team used an independent statistical consultant for all data analysis, and that two additional outside investigators from two other academic institutions confirmed their findings.
“As you can see, we have done everything possible to ensure the integrity of the data. My co-authors and I stand by our published findings,” she says. “The comprehensive nature of the current study underscores why the findings from the pilot study should be interpreted with an abundance of caution, given the small number of animals included.”
But Sallie Bernard, president of SafeMinds, says she would at least like to see a re-analysis of the newest data. “We feel that embedded within these data sets there are animals that have potentially an adverse reaction to this vaccine schedule that would mirror what happens in human infants,” she says. “The majority who get vaccines are fine, but we believe there is a subset that have an adverse reaction to their vaccines. By looking at the raw data, not data in aggregate, we may be able to identify the subgroup that had that reaction.”
Halladay commends SafeMinds for financially supporting the study, but she worries that some autism advocates may be asking the wrong questions. “I'm not saying that we need to stop funding research in the environment, because we know the environment does impact neurodevelopment,” she says.
Halladay likens the challenge of disputing the claim that vaccines cause autism to “playing whack-a-mole.”
“First, the proposed association was between the MMR vaccines and autism,” she says. “Then that was disproven. Then it was the thimerosal components in vaccines; now that has been further disproven in a carefully designed animal model study that aimed to specifically examine that question. It has also been suggested that the association is because of vaccine timing, but that too has been disproven. The target always seems to be moving, and the expectation is that scientific resources will be diverted to address each new modification of this hypothesized link.”